Many occupations require workers to be on duty around-the-clock for extended periods of time, and to work irregular shifts while on duty. However, night work and/or irregularly scheduled shifts can lead to worker fatigue, which is defined here as reduced alertness, increased sleepiness, impaired performance or unsafe behavior occurring as a result of excessive work hours, inadequate rest, sleep deprivation or circadian time-of day factors. In addition, workers often suffer acute or chronic sleep deprivation, in combination with circadian time-of-day factors, which can exacerbate fatigue. Worker fatigue is particularly problematic among transportation employees including commercial motor vehicle (CMV) operators, for example, truck drivers, wherein driver fatigue can increase the risk of an accident.
Many governments recognize this issue, and have implemented prescriptive rule-based regulations in an effort to reduce the number of accidents caused by worker fatigue. For example, in the United States, the Federal Motor Carrier Safety Administration (FMCSA), to reduce the number and severity of commercial motor vehicle (CMV) crashes and enhance the safety of CMV operations, has implemented Hours of Service (HoS) regulations which place maximum limits on the number of hours of work, and minimum limits on the hours of rest. HoS regulations are widely adopted in all transportation modes including the regulation of commercial motor vehicles. However, prescriptive HoS regulations do not distinguish between off-duty time and actual sleep time. Instead, contrary to its intended purpose, HoS regulations often require CMV operators to operate their vehicles when they are fatigued, and to stop driving at times when they are not tired and cannot sleep. This can lead to drivers falsifying their driver logs so that they can sleep when they are tired, and drive when they are alert. While advances in circadian, sleep and alertness physiology, and the technology and operations of modern transportation address have been used to attempt to address shortcomings of prescriptive HoS regulations, the interaction of circadian sleep science and modern operational practices is highly complex, and it is impractical to adequately overcome such shortcomings by incorporating operational practices based on circadian sleep science into current prescriptive HoS regulations.